Who has the best photo of an animal's genitalia? The only way to find the answer is with a good ol' fashioned "junk-off".

Yesterday, the hashtag #JunkOff was spawned following some purely innocent and scientific photos posted by the Wildlife Habitat and Population Analysis Lab (WHAPA). According to Gizmodo, biologist Anne Hilborn and her colleagues at the Department of Fish and Wildlife Conservation at Virginia Tech began adding pictures of animal genitalia to the Twitter account. As more photos were added, one of their followers called it a Junk-off and the idea stuck.

Hilborn tweeted "ATTEN: WE ARE HAVING A JUNK-OFF" and so it began.

While the junk-off started with expected entries, such as zebra and elephant penises, soon followers were reminded of the great diversity of the animal kingdom.

Contributors have used the hashtag as a chance to educate, highlight the species they study but mostly get in on the fun.

Even our own Herpetological Society of Ireland got in on the act with a saltwater crocodile penis.

If you've ever wondered what a bat's penis looks like, well, it's there. Or perhaps you needed to know that black widows have corkscrew-shaped emboli which break off inside the female. A quick look at the junk-off will confirm everyone's suspicions: "damn nature, you crazy!"